The present invention relates to a brushless linear rotary transformer. The a brushless linear rotary transformer commonly used as a sensor to determine angular position and velocity of an output shaft, and applied in servo control systems. The disclosed sensor can also be used in coordinate transformation, triangle operation, transmission of angle data, and in measurement of the displacement of a vibrating body.
As angular position sensor, the rotary transformer is widely used in servo control system. In addition to rotary transformer, the optical and magnetic encoders are also used to determine angular position of an output shaft. The optical encoder converts angular displacement of the rotating shaft into the digital pulse signals. According to the lithography method and output signal, the optical encoders are further divided into incremental and absolute encoders. Incremental encoder has the advantage of simple structure, being able to give information of angular position in the incremental manner. Yet this kind of optical encoder is failed to indicate the initial angular position. Absolute encoder directly provides the absolute angular position of an output shaft. However, absolute encoder has complex structure. Applications using optical sensor devices are technology limited with regard to accuracy, tend to be expensive, and sensitive to environmental conditions, and can be corrupted by opaque contamination. Due to the fragility of glass, optical encoder can not be applied to determine high angular velocity.
Magnetic sensor is another kind of apparatus used to determine angular position of an output shaft, which operates by changing magnetic pole. Applications using magnetic sensor devices are limited by poor accuracy.
The rotary transformer is a kind of electromagnetic induction sensor used to determine angular position of an output shaft. Prior rotary transformer for sensing the angular position and velocity includes a rotor, a stator, and pairs of inductive coils. The coils mounted in the stator are the primary coil windings, which are connected to receive the excitation signals, whereas the coils wrapped around the rotor are the secondary coil windings, which output the induced electromotive forces. The rotary transformer has the simple and reliable structure, which is particularly applicable in harsh environment that other kinds of sensors fail to work.
According to signal output manner from the coil winding wrapped around the rotor, the rotary transformers used to determine angular position are divided into rotary transformer with brush, wherein the signals from the coils wrapped around the rotor are output through slip ring and brush, and brushless rotary transformer. Applications of the rotary transformer with brush are subject to wear, friction, and vibration.
Prior brushless rotary transformer has two different configurations, one is toroidal type transformer and the other is reluctance type transformer. In prior toroidal transformer, a coil winding wrapped around the stator and a coil winding wrapped around the rotor are concentrically arranged and electrically connected. Signal input and output are performed by the toroidal transformer. In prior reluctance type transformer, both excitation winding and output winding are embedded within the same set of slot distributed in the stator. Signals at excitation winding and output winding are sine and cosine functions of the angular position of a rotating shaft, with a phase shift of 90 degrees. Special design and processing are required for manufacturing the magnetic pole of the rotor in prior reluctance type transformer, so that the magnetic field in an air gap between stator and rotor is the sine or cosine function of the angular position of the rotor. Applications using prior brushless transformers are technology limited with regard to complex mechanical structure and difficulty in manufacture.
The relative position of the primary coil winding and the secondary coil winding is changed with angular displacement of the rotor in prior devices. The relation between an amplitude of the signal at secondary coil winding and the angular position of the rotor is a sine or cosine function, or a linear function in a restricted range of the angular position. Applications of single pole rotary transformer are limited by poor accuracy. In order to improve measurement precision, a plurality of pairs of magnetic poles are usually embedded in prior rotary transformer, which inevitably increases the complexity and reduces the reliability of the device.
The primary coil winding in prior device outputs two orthogonal analog signals, whose amplitudes are sine and cosine functions of the angle of the angular position of the rotor. In order to obtain the angular position of the output shaft, it is necessary to design and fabricate particular and expensive electrical circuits for modulating and demodulating signals. Particular integrating circuits, such as AD2S1200, AD2S1205, and AD2S1210 fabricated by Advanced Micro Devices, Inc., are usually needed. Applications of prior art devices are limited by poor accuracy and high price.
Accordingly, a need remains for a reliable and accurate angular position sensing device of improved manufacturability, operating performance, and simplified signal treatment.
The present invention provides a brushless linear rotary transformer, which can overcome the limitations of prior art devices for sensing the angular position. The apparatus of the present invention has the advantages of simple and reliable structure, with strong anti-interference ability. No particular and expensive circuit is needed in the present invention for modulating and demodulating signals. The apparatus of the present invention can be used to accurately determine the angular position and velocity of an output shaft in multiple turns.